This application claims the priority of Korean Patent Application No. 2005-82787, filed on Sep. 6, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a WiBro system and, more particularly, to a method and apparatus for detecting minute oscillation in a WiBro repeater, and a WiBro repeater having the same.
2. Description of Related Art
A wireless broadband (WiBro) system provides high-data-rate wireless Internet access under the stationary or mobile environment, anytime and anywhere. A currently available mobile phone provides a wide coverage area and high mobility, but fails to provide IP-based high-speed data service efficiently. On the contrary, high-speed Internet and wireless LAN supports the IP-based high-speed data service, but provides a narrow coverage area and low mobility. On the other hand, the WiBro system that provides IP-based content is more economical compared to the mobile phone. Further, the WiBro system can provide a wider coverage area compared to the high-speed Internet or wireless LAN, and is suitable for a mobile communication environment.
In the WiBro system, repeaters are used to eliminate indoor dead spots and to improve service quality in areas where portable Internet services are provided. The repeaters are installed in buildings or in poor service areas between portable subscriber stations (PSS) and radio access stations (RAS) to repeat radio wave so that the service quality can be improved and the dead spots can be eliminated.
Since an input signal is amplified and output by the repeater, the input signal should be sufficiently isolated from an output signal to prevent the output signal from being fed back to the input signal thereby causing oscillation. Oscillation causes the input signal to increase, thereby damaging the repeater. Thus, oscillation should be detected before it occurs, and it should be prevented by reducing amplifier gain. Oscillation occurring due to feedback of part of an output signal to an input signal is referred to as minute oscillation. The minute oscillation should be detected beforehand to prevent the repeater from being damaged.
FIG. 1 is a graph showing a spectrum of a fading channel when minute oscillation occurs.
Minute oscillation can be detected by monitoring a spectrum of an output signal and measuring a difference between maximum and minimum values of the spectrum. However, this can be carried out only in a laboratory since a spectrum analyzer is required. In addition, since the difference between the spectrum values is not constant in an actual fading channel as shown in FIG. 1, it is not possible to detect the minute oscillation only by measuring the difference between the spectrum values.
FIG. 2 is a graph showing an OFDMA spectrum when minute oscillation occurs.
A WiBro system employs an Orthogonal Frequency Division Multiple Access (OFDMA). OFDMA works by assigning a subset of subcarriers to individual users. Data may be assigned only to some subcarriers. Thus, when data is present only in some subcarriers as shown in FIG. 2, it is not possible to determine whether or not minute oscillation occurs only by monitoring the spectrum.
Meanwhile, another method of detecting the minute oscillation is to extract a multipath and check whether or not there is a multipath corresponding to loop delay. However, the method has a problem that since information concerning a signal inputted to extract the multipath is required, the method can be applied to a signal including a preamble but not to a signal having no defined data, such as an uplink.